CHEMILUMINESCENCE FROM ACTIVATED HEME COMPOUNDS DETECTED IN THE REACTION OF VARIOUS XENOBIOTICS WITH OXYHEMOGLOBIN - COMPARISON WITH SEVERAL HEME HYDROGEN-PEROXIDE SYSTEMS

Chemiluminescence was detected in the reaction of oxyhemoglobin with v arious hydroxylamines and phenols, which have previously been shown to produce free radicals. The emitted light intensity correlated roughly with the methemoglobin formation rate, indicating the involvement of a photoemissive species as a reaction intermediate. In our previous wo rk, we postulated the involvement of a catalase-insensitive, heme-boun d hydrogen peroxide species in the methemoglobin formation reaction. I n a series of experiments, we showed that intensive chemiluminescence occurred when hydrogen peroxide was mixed with either methemoglobin or metmyoglobin but not with hematin, which lacks the globin moiety. Thi s suggests the involvement of the globin moiety in the light-emitting reaction sequence. The detection of paramagnetic globin species exhibi ting similar kinetics as the corresponding light-emitting compound dem onstrated that the assumed H2O2-heme compound has strong oxidizing pro perties. Accordingly, addition of bovine serum albumin to the hematin- hydrogen peroxide system also resulted in a strong chemiluminescence d ue to the formation of a paramagnetic transient species which could be detected by electron spin resonance (ESR). Several other heme compoun ds. such as cytochrome c or cytochrome c oxidase which have no vacant ligand site, did not show any light emission under similar conditions. This means that hydrogen peroxide must have access to a free-binding position on the heme. Chemiluminescence most probably stems from the t ransition of the initially formed heme-H2O2 adduct to the compound II type species. Due to their oxidizing nature, these species might be re sponsible for deleterious toxic effects such as lipid peroxidation and protein degradation.